by adding this to mysite/_config.php
// Define which payment methods your site uses.
'ChequePayment' => 'Cheque Or Pay On Site',
'PayPalPayment' => 'PayPal (Credit Card)'
but getting a few errors when trying to configure the rest of paypal with my account information.
The PayPalPayment class thats packaged with the ecommerce plugin doesn't seem to be complete.
There is this old one form about 2 years ago it seems, which I don't think is compatible any more http://open.silverstripe.org/attachment/ticket/1760/PayPalPayment.php